This section illustrates useful background information without admission of any technique described herein representative of the state of the art.
Portable devices of different types are used in modern societies for various purposes such as communications, entertainment, imaging and navigation. Some devices can be further enhanced or their use be facilitated by physical accessories such as add-on lenses, replaceable color covers or even smart covers that provide a portable device, when attached, with new features or functionalities such as a near field communication circuitry or wireless charging capability.
As the number of various items used by a person increases, it is increasingly more difficult to access at sudden need a given one. Therefore, different accessories are integrated with portable devices as much as possible. For example, some very high-end camera phone model contains a built-in neutral density (ND) filter that is automatically used in excessive ambient light to increase the exposure time when the optics would otherwise be too fast or when a longer exposure time would produce more pleasing effects in photographs.